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Using Calibration to Optimize Performance in Crucial Measurements
The new R&S ZNB family of network analyzers stands out due to its wide dynamic range of up to 140 dB (at 10 Hz IF bandwidth), its low trace noise of 0.004 dB (rms) (at 10 kHz IF bandwidth) and its high output power of up to +13 dBm that can be varied electronically in a range of more than 90 dB. The state-of-the-art operating concept of these network analyzers makes configuration, measurement and analysis simple.
All basic and frequently used functions can be controlled via keys, and functions needed for the individual test sequences are available via context-sensitive menus on the touch screen. Working with diagrams and traces, setting up markers for analysis, and zooming in on details—all it takes is a simple movement of the finger on the large, high-resolution 12.1- inch screen. Due to their shallow depth, the compact two-port and four-port analyzers leave plenty of space on the workbench for the measurement application.
Operation is extremely low-noise thanks to low power consumption and an elaborate cooling concept. With the available frequency ranges of 9 kHz to 4.5 GHz and 9 kHz to 8.5 GHz, the network analyzers are primarily intended for use in the mobile radio and wireless communications and electronic goods industries. The R&S ZNB is suitable for developing, producing and servicing RF components such as amplifiers, mixers, filters or cables, which are often used in large quantities by manufacturers of base stations and mobile terminal equipment.
The R&S ZNB does away with side and submenus and, in addition to hard keys and soft keys, it includes a soft panel as a new control element. The soft panel not only displays control functions that may be needed for a measurement, but also supports all instrument functions at the press of a maximum of three keys. The analyzers of the R&S ZNB family offer tangible network analysis as they allow users—simply by touching the screen—to shift traces between diagrams, position markers on traces, move scaling reference lines, or change test parameters via context-sensitive menus right at the point where the parameters are displayed.
Figure 1 R&S ZNB control elements.
Measurement tasks such as characterizing amplifiers and RF modules, which involve a large number of test parameters, can be split up and assigned to several clearly arranged instrument setups with just a few traces. All instrument setups are available at a finger’s touch, and because there are no submenus, each step that needs to be performed is clearly accessible on the touch screen. This straightforward operating concept (shown in Figure 1) not only benefits untrained or infrequent users, but also makes operation easier for experienced users and increases measurement efficiency.
Figure 2 R&S ZNB language selection.
The R&S ZNB offers users a wide choice of options when it comes to displaying results. Traces can be freely assigned to diagrams and channels, and assignments can be changed at any time during the measurement. To maximize the display area, which may be a useful option during manual adjustments, the soft panel can be hidden to make the entire screen area available for displaying results. Recognizing that solving a wide variety of tasks is easiest in one’s mother tongue, the new network analyzers offer a large range of language options, including English, Chinese, Japanese, French and Russian (see Figure 2).
Fast or accurate? This is often a question faced by users in a production mode. However, with the R&S ZNB there is no longer the need to trade off speed against accuracy as the network analyzer combines a fast synthesizer with high sensitivity and a wide dynamic range.
The speed of measurements involving high attenuation—for example in the stopband of a base station duplex filter—is determined by the required dynamic range and the corresponding IF bandwidth. Reducing the IF bandwidth by a factor of 10 will increase the dynamic range by 10 dB. In the case of narrower IF bandwidths, the measurement time per point is approximately 1/IF bandwidth. The larger the IF bandwidth, the shorter the measurement time.
A 10 dB increase in dynamic range will boost measurement speed by a factor of 10. The R&S ZNB offers a dynamic range of up to 140 dB at 10 Hz IF bandwidth. At a dynamic range of 120 dB, the measurement time per point is therefore 1 ms. In addition to high measurement speed, this also offers a signal-to-noise ratio (SNR) sufficient to provide high measurement accuracy. Figure 3 shows filter measurements at 10 Hz IF bandwidth.
Figure 3 Filter measurement at 10 Hz IF bandwidth.
Measurements involving low attenuation—for example in the passband of a base station duplex filter —can be carried out at maximum IF bandwidth. Measurement time is not determined by the IF bandwidth, but by the speed of the synthesizer. At an IF bandwidth of 1 MHz, the R&S ZNB requires no more than 4 ms for a sweep with 401 points. The measurement error is virtually negligible even at this high IF bandwidth due to the low trace noise. Figure 4 shows the trace noise at 10 MHz IF bandwidth 0.1 dB.
The R&S ZNB supports a variety of different calibration methods. The Un-known Through, Open, Short, Match (UOSM) calibration method deserves a special mention as it supports simple calibration kits that do not contain a Through standard. Calibration with such kits is carried out using a simple adapter not known to the vector network analyzer instead of a high-quality Through standard.
Figure 4 Trace noise at 10 MHz IF bandwidth is less than 0.1 dB.
While such adapters are inexpensive, they lead to measurement uncertainties of up to a few tenths of a dB with calibration methods requiring Through, Open, Short and Match standards. When using the UOSM method, the adapter’s characteristics are irrelevant, and accuracy after calibration is comparable to that achieved with a high-quality Through calibration standard.
For applications calling for speedy calibration, e.g. in production, the R&S ZNB supports automatic calibration units. Controlled via USB, these units carry out full calibration within 30 sec of the press of a key. This affords an enormous speed advantage and minimizes the risk of operator errors over manual calibration especially when full four-port calibration is performed, e.g. on balanced two-port components. Figure 5 shows the R&S ZV-Z51 calibration unit.
Figure 5 Calibration unit for the R&S ZNB.
Careful calibration increases measurement accuracy, but interrupts the development or production process. As temperature and long-term stability determine the calibration interval, the R&S ZNB hardware has been developed with these factors in mind. Good raw data is also crucial to stability. This data indicates a network analyzer’s accuracy when no internal error correction is active and no user calibration has been performed. The new network analyzers offer raw test port match of up to 25 dB and directivity of up to 35 dB.
The R&S ZNB offers a wealth of functions for measuring amplifiers. In addition to S-parameters, it determines output power, stability factors, power consumption, impedances and Z-parameters as a function of frequency or power. The high output power of up to +13 dBm and the wide electronic power sweep range of over 90 dB enable fast and wear-free amplifier measurements under different stimulus conditions.
The electronic receiver attenuators are designed for input powers of up to +27 dBm, enabling the network analyzer to perform compression-free measurements even on amplifiers with high output powers. Amplifier characterization also includes determining the RF to DC transfer characteristics of power-monitoring level detectors and measuring power consumption to determine efficiency. For this purpose, the R&S ZNB offers four DC inputs with a voltage range of ±10 V and sensitivity of 10 µV. With future proofing in mind, the R&S ZNB supports the remote control command sets of other Rohde & Schwarz network analyzers and those of other manufacturers’ instruments.
Productivity redefined—the new R&S ZNB network analyzers feature simple operation, flexible analyses, long-term stability, high IF bandwidths and a dynamic range previously found only in high-end instruments. Whether in production or development, they offer enhanced measurement speed and reliable accuracy at reduced calibration effort and support users in optimally organizing their measurement processes. The two-port model is available with four-port models coming online in September 2011.
Rohde & Schwarz,
+49 89 4129 12345,
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